Field
The disclosed concept relates to electrical switching apparatus, such as, for example, circuit breakers and, more particularly, to circuit breakers employing a slot motor. The disclosed concept further relates to slot motors.
Background Information
Electrical switching apparatus, such as circuit breakers, are employed in diverse capacities in power distribution systems. A circuit breaker may include, for example, a line conductor, a load conductor, a fixed contact and a movable contact, with the movable contact being movable into and out of electrically conductive engagement with the fixed contact. This switches the circuit breaker between an ON or closed position and an OFF or open position, or between the ON or closed position and a tripped or tripped OFF position. The fixed contact is electrically conductively engaged with one of the line and load conductors, and the movable contact is electrically conductively engaged with the other of the line and load conductors. The circuit breaker may also include an operating mechanism having a movable contact arm upon which the movable contact is disposed.
Upon initial separation of the movable contact away from the stationary contact, an electrical arc is formed in the space between the contacts. The arc provides a means for smoothly transitioning from a closed circuit to an open circuit, but produces a number of challenges to the circuit breaker designer. Among them is the fact that the arc results in the undesirable flow of electrical current through the circuit breaker to the load. Additionally, the arc, which extends between the contacts, often results in vaporization or sublimation of the contact material itself. Therefore, it is desirable to extinguish any such arcs as soon as possible upon their propagation.
To facilitate this process, circuit breakers typically include arc chutes which are structured to attract and break-up the arcs. Specifically, each arc chute includes a plurality of spaced apart arc plates. As the movable contact is moved away from the stationary contact, the movable contact moves past the ends of the arc plates, with the arc being drawn toward and between the arc plates. The arc plates are electrically insulated from one another such that the arc is broken-up and extinguished by the arc plates.
In order to successfully interrupt a DC circuit, the circuit breaker needs to generate an arc voltage higher than the system voltage to stop the current flow. A challenge with interruption is that there is often not enough current-induced magnetic force and gas dynamics to force the arc into the arc chute. One known approach to address this issue involves the placing of large permanent magnets in the arc chute to drive the arc into the arc chute. However, among other disadvantages, large permanent magnets are costly and significantly increase the size of the arc chute.
There is thus room for improvement in electrical switching apparatus and in slot motors therefor.